Different processes are known in the art for reducing or eliminating the combustibility of thermoplastic polymers. Some of these processes are based on the use of metal compounds, especially antimony, bismuth or arsenic compounds, in combination with partially halogenated and thermally unstable organic compounds, such as, for instance, chlorinated paraffin waxes.
Other, more recent processes are based on the use of organic or inorganic phosphorus compounds in combination with nitrogen-containing organic compounds, in general a resin obtained by condensation of urea, melamine or dicyandiamide with formaldehyde.
These latter retarding systems confer to the polymer that contains them the property of giving place to the formation of a carbonaceous residue following a fire or attack by flame.
The retarding systems of this kind offer several advantages: absence of corrosion phenomena in the machinery on which the polymers are processed; a lower specific weight of the polymeric compositions in comparison with those containing metal compounds and halogenated hydrocarbons, and, above all, the possibility of conferring to the polymers satisfactory anti-flame properties with a lesser quantity of total additive and, thus, without an excessive decay of the mechanical properties of the polymers themselves.